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The results of analytical and experimental investigations to develop efficient and reliable water injection methods for reducing the nitrogen oxides (NOx) levels of the LM2500 and LM5000 engines are presented. These aircraft-derivative turbine engines are equipped with compact annular combustors. In these investigations, various methods of injecting water into the combustor primary zone were evaluated in combustor and engine tests to identify methods with minimal water flow requirements for a given degree of NOx abatement. Primary emphasis was focused on the development of methods of injecting liquid water into the engines when operating with distillate fuels. Methods of injecting both liquid water and steam when operating with natural gas were also investigated. The impacts of water injection on combustor and engine performance and operability were additionally assessed. Satisfactory accommodation of water/fuel weight ratios above unity and associated NOx level reductions as high as 90 percent were demonstrated.

Within recent years, the NOx emissions of aircraft engines have received increased attention. More stringent limits on the NOx emissions of future subsonic civil aircraft engines are being considered. A 20 percent increase in the stringency of the existing ICAO standard has been proposed and, for the longer-term, the possibility of further increased stringency is being studied. For future supersonic civil aircraft engines, very stringent goals have been established. To meet these goals, combustor designs with ultralow NOx levels are required. Extensive efforts are, therefore, underway to develop low NOx combustors for use in future generations of both subsonic and supersonic aircraft engines.

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